Aircraft instrument



March 24, Q L E BAYNEYS I AIRCRAFT INSTRUMENT I Filed Mairch 5, 194;

:raft instruments audit is an Patented Mar. 2 1942 UNITED STATES PATENT OFFlCE--.

aracaarr INSTRUMENT I Leslie Everett Baynes,

signor to Hounslow, Pa y Iver Heath, England. as-

Alan Muntz Middlesex, EnglantLa British com- & Company Limited,

Application March 5, 1941, Serial No. 381,923 In Great Britain February 20, 1940 5 Claims. (Cl. 13-152).

This invention comprises improvements in airobject of their;- vention to provide an instrument which will indicate to the pilot the stalling speed and the change of the stalling speed under varying conditions.

The stalling speed of any particular aircraft is a determinable quantity for the case of steady flight and it is usually marked up somewhere in the cockpit within view of the pilot, and the latter is careful to fly at a safe margin above this craft, a device to apply speed. The bare statement of this speed,how-

ever, is misleading because when an aircraft is pulling out of a dive or is turning with a steep angle of bank the stalling speed is not the same as when the craft is in steady flight.

The reasons for this are as follows:

As is well known the stalling speed of an aircraft is proportional to the'square root of the,

wing loading. when turning sharply or pulling out of a dive the wing loading is considerably iiicreased and therefore the stalling speed is also increased. Considered mathematically, if 9 represents the force exerted by gravity per unit of. mass and a represents the force exerted perunit of mass by acceleration forces due to turning or the total force per unit of pulling out of a dive, mass which is to be borne by the aerofoil surfaces of the craft is the vector sum of g and a, and this may be called G. Since'the wing loading is proportional to G the stalling speed is proportional to the square root of (Ii.

Thus, a high speed aircraft making a small radius turn, necessitating a steep angle of bank. may have a value for G which is as much as six times g, during the turn. The stalling speed therefore durlng the turning manoeuvre will in this case'be increased in the proportion of particular aircraft, which may stalling speed actually is when any manoeuvre is being carried out.

,According to the present invention a stalling speed indicator comprises a mass which'is movable under the combined efiects of gravity and additional acceleration due to manoeuvring the a controlling force tending to counteract movement of the mass and means to indicate the extent of movement of the mass thereby giving readings which are a function of G.

' The indicator may'serve particular to give readings on any be graduated to read directly in terms of thestailing speed.

Preferably, characteristics of the control for the mass and of the indicating means are such as to give a scale of readings which is uniformly spaced for uniform increments of stalling speed. In such a case it becomes possible to combine the stalling speed indicator of this invention with the usual air speed indicator of the craft. This may be efiected by utilising as the stalling speed indicator a pointer which is concentric with the air speed indicator and moves over thesame scale thereby giving an easily visible indication to the pilot of the margin of speed which he has in his actual flying speed over and above the prevailing stalling speed.

In order that the invention may be more clearly understood one preferred construction will now various parts necessary in a stalling speed indicator according to this invention. 1

A small weight i0 is carried at the end ofan arm Ii which is rigidly connected at i2 toa VF=2A5 times normal stalling sipeed (flaps up) This is equivalent on a modern aircraft to about 200 miles per hour, and asi the flying speed may not be much above this figure there is the danger of a stall taking place on theinner wing; that is to say, the one on the insidejof the radius. which is flying'more slowly relatively to the air than the average speed of the craft. The -machine may thereforeflturn any warning. The same; thing may happen when pulling out of a dive, that is to say, the -stalling speed may increase two or three times the normal value due to the increase in the value of G. Theresult may bethat instead oi pulling out of the dive the machine .will'stall and hit the ground or sea.

It is,-there fore, very desirable that the pilot should have some means of knowing what his into a spin without sector It. The latter is free to turn about apivot it so that the weight in is free to move substantially in a vertical direction when the craft is v flying horizontally on an even keel. The weight is a cam plate I! having spindle 23 to turn about the axis of that spindle is sustained against downward movement by a helical tension spring 15' and will move Aipv or down in accordance with the value of G. Sector l3 has teeth It at its periphery which mesh with a pinion l1 rotating on a fixed spindle -l8.- Secured to rotate incompany with the pinion i'l formed in it acam slot 20. Engaged in the slot is a cam follower 2| comprising a small wheel rotatably'mounted on the end of lever 22. The latter is mounted on a in company with a spur wheel 24. The-latter drives a pinion 2izsxrotatable with a=-spindle 28 through the intermediary of a pinion 2'l and spur tinguish it from movement can be used.

wheel 28 both mounted to rotate about the axis of a spindle 29.

Rotatable with pinion 25 is. a pointer friction-tight upon the spindle 28 constituting the stalling speed indicator and the shape of cam 2'0- is such that movement imparted to the pointer 30 through the gearing Just described will be propreferably coloured sdiflerently so as readily to distinguish be- For example, pointer 80 may be Soshaped as to represent a line ot rather than a. pointer. If

indicator 3| normally of the luminous type pointer" 30 mayhave a luminous spout-at-its end 'to dispointer 3| which will generally be luminous throughout the major portion of its length, or any other preferred'means may be utilised to distinguish between the two pointers lorindicators 730 and 3|. I

If the air speed indicator 3| moves back to a ,po'sition in which it is coincident with the stalling speed pointer 30- this will show that the stalling speed has been reached and during the approach towards this superposition of the pointers the pilot is given an easily visible warning of the approaching danger of stalling.

The setting of the stalling speed indicator relatively to the scale and to its actuating mechanism is made adjustable by the friction-tight mounting of the pointer 30 so that it can be set, for any particular aircraft, at the known steadyflying stalling speed of the machine.

As is well known, 11' G reaches a high figure, which varies with different individuals, the pilot loses blood fromthe brain and therefore loses consciousness, which is known as blacking out." It will be appreciated thatthe instrument described, in-addition to giving indications of stallthe pilot warning of the approach of blacking the approach of the the pointer from Is, 20, 2|, 2: for

' impart to the pointer the square root of the distance moved by the loading of the inaone proportional to the movement of the weight into one proportional to the If the. speed scale of the air speed indicator square root of its air speed indicator having the square root of is not truly proportional to air speed, i. e. if the graduations vary in spacing from one of the. scale to another, the stalling speed indicator would need to be modifledaccprdlngly, but a' truly linear scale is necessary ment is to be used for different-type machines ving different settings for stalling speed.

1. In or for an aircraft the combinationof an an air speed scale and a pointer moving thereover, a stalling speed indicator mechanism having a mass movable under the combined eflects of gravity and additional acceleration due to manoeuvring the craft, a device to apply a controllingforce tending to counteract movement or the mass. a pointer having operative connections with said mass to indicate the extent of movement of the mass, which pointer is concentric with and works over the same scale as the air speed pointer, said device to apply a controlling force and said connections being such as to cause the stalling speed pointer to indicate stalling speed correctly on the air speed scale.

2. A stalling speed indicator as claimed in claim 1 in which the device to apply a controlling force to the-mass comprises a spring tending to resist movement of the mass and said connections include a cam coupled to the mass to move with it, the shape'of the cam being such as to movement proportional to the square root of the distance moved by the mass.

3. A stalling speed indicator comprising in combination a stalling speed pointer, a mass rotatable about a fixed axis eccentric to itself, a

cam rqtatable about a second axis, gearing inter-l able arm engaged with the cam and means operatively interconnecting the arm and said stalling speed pointer. 1

4. A stalling speed indicator as claimed in claim 3, wherein the cam is of such. shape as to impart to the pointer movement proportional to mass.

5. A stalling speed indicator as claimed in claim 3, wherein the cam is of such shape as to impart to thepointer movement proportionalv to the distance moved by the mass and wherein said indicator is mounted in an air speed indicator casing with the pointer concentric with an .air speed pointer of the air iftheinstru-' 

